I have a ASM1164 PCIE3 x2 SATA card with two SSDs connected to it. During large transfers between the two drives, I started noticing a pattern of my web browser's (Edge) performance being affected. For some pages, scrolling would become slow and even lock up altogether. At first, I didn't put two-and-two together (why would I?) but then I noticed that as soon as I cancelled the data transfers, the browser would immediately become responsive again. The issue is a little inconsistent in its manifestation, but I've now repeated this enough times to be sure it's not a coincidence. Somehow there is a relationship between the drives on the card and the browser.
I went looking for bottlenecks. The drives are unencrypted, and the CPU is barely being taxed even when the browser is practically frozen. The performance of the drives themselves is unaffected. The RAM is less than half occupied. The PC isn't cutting edge, but it's not terrible either (6700K, z170x, 32GB) and the transfers between the drives are only 200-400MB/s. What's more, the ASM1164 card is on the CPU's PCI-E lanes, NOT the PCH. The GPU is also on the CPU, so its running at 8x, but it's a GTX 960 and barely even being utilized.
I know this is a long shot, but does anyone know what could possibly be causing this behavior?
TL;DR: During large SSD transfers through ASM1164 card, Edge browser gets bogged down. Cancelling transfer immediately restores Edge performance.